This invention relates to a toroidal type continuously variable transmission (referred to hereafter as CVT) used in a vehicle or the like, and to a method for manufacturing a link thereof.
Japanese Patent Laying Open Publication Heisei 7-174201 published in 1995 discloses the CVT. In this CVT, mutually opposed power rollers are interposed and held between coaxially disposed input and output disks. Further, trunnions which support the shafts of these power rollers are supported so as to be capable of displacement in the axial direction as well as rotatable around their axes.
With this type of the CVT, the upper ends and the lower ends of the trunnions, which are provided as mutually opposed, are respectively connected together by an upper link and a lower link. Due to this, when a trunnion is displaced along its axial direction, the upper link and the lower link execute swinging movement. At this time, shoulder portions formed upon the trunnions and projecting portions on the upper link or on the lower link may come into contact with one another.
If the projecting portions of the links are formed as sharp corner portions, these corner portions often bite at the shoulder portions of the trunnions when they contact slidably into the shoulder portions of the trunnions. Due to the occurrence of this biting, the movement of the trunnions, in other words the gyration movement of the power rollers, is obstructed, which causes resistance during speed changing. As a result this becomes a cause of hysteresis in the speed change characteristic of the transmission.
Further, if a variation should be present in the shapes of the corner portions, then the sliding resistance set up to the movement of each of the trunnions undesirably becomes different. That is to say, when the projecting portions contact slidably into the trunnions, although one of the trunnions may gyrate easily, it may happen that the other trunnion cannot gyrate easily due to biting of the corner portions. Accordingly, the problem has occurred of hysteresis being engendered in the speed changing characteristic due to variation of the sliding resistance acting in the directions of gyration of the power rollers, which causes deterioration in the accuracy of speed change control.
The objective of the present invention is to prevent the occurrence of hysteresis in the speed change characteristic by rendering uniform the contact condition of the links and the shoulder portions of the trunnions.
In order to achieve above object, this invention provides a toroidal type continuously variable transmission, comprising: a rotation shaft; input disks which are arranged coaxially with said rotation shaft and is driven thereby; output disks which are arranged coaxially with said rotation shaft and opposes said input disks; a pair of trunnions arranged in opposite positions on both sides of said rotation shaft and movable in its axial direction of said rotation shaft and also around its axial direction of said rotation shaft, each said trunnions comprising rotation shafts formed at both end portions of said trunnions, and offset portions which are offset by a predetermined amount from said rotation shafts between said trunnions and said rotation shafts; an actuator which drives each of said pair of said trunnions in the mutually opposite axial direction of the trunnions; power rollers which are supported by said trunnions and are gripped between said input disk and said output disk; links each of which is respectively formed with aperture portions into which said respective rotation shafts of said trunnions are inserted; and spherical joints provided between the outer peripheries of said rotation shafts and said through holes; shoulder portions formed on said trunnions opposing said links; and projecting portions formed upon said links and capable of contacting slidably into said shoulder portions of said trunnions when said links execute swinging movement; wherein end portions of said projecting portions are formed with arcuate faces.
Further this invention provides a method for manufacturing a link for a toroidal type continuously variable transmission, wherein said link is provided with aperture portions at its both ends through which said rotation shaft portions of said trunnions are passed, and with projecting portions which can contact slidably into said shoulder portions of said trunnions when said trunnions execute swinging movement, and end portions of said projecting portions which contact slidably into said shoulder portions of said trunnions are formed with arcuate faces.